When the voltage drops below 10% of
its nominal value it is called an interruption or a blackout.
Interruptions have three classifications: momentary (lasting 30 cycles
to 3 seconds), temporary (lasting 3 seconds to 1 minute) and sustained
(lasting more than 1 minute). Although interruptions are the most
severe form of power problem, they are also the least likely to occur.
Voltage sags are often mistaken for an interruption because equipment
shuts down or lighting goes off since the voltage dropped below the
point that these devices can operate. Where sags and undervoltage
typically represent more than 92% of power problem events,
interruptions represent less than 4% of such problems. |